Low cross-linking-density gel and process for producing the same

ABSTRACT

A process for producing a low cross-linking-density gel capable of effectively inhibiting light scattering in joining the ends of optical fiber cores with each other. The process is characterized by involving the compounding step for adjusting a flexible silicone gal material to have a specified refractive index and the reaction step for cross-linking the flexible silicone gel material obtained in the above step in a binding region with a low cross-linking density, thus yielding a low cross-linking-density gel.

FIELD OF TECHNOLOGY

The present invention relates to a low cross-linking-density gel used asan optical conductor for connecting end faces of optical fibers, and amethod for producing such a gel.

TECHNICAL BACKGROUND

An optical fiber connector, a fixed connecting device, a lightcombining/splitting device or like device has been generally used toconnect end faces of optical fibers.

A mechanical contact method is mainly used to connect end faces ofoptical fibers in an optical fiber connector. According to thismechanical contact method, ferrules are respectively fitted on cores ofboth optical fibers and are inserted into fitting holes, which areformed in the opposite side surfaces of a connector main body tocommunicate with each other in linear alignment with each other, fromthe opposite sides of the connector main body, and the end faces of thetwo cores having the ferrules fitted therearound are fixed in abutmentagainst each other to be connected with each other.

Besides the above mechanical contact method, for example, there havebeen proposed the use of a lens as an optical conductor at a jointportion and the use of a matching oil in the optical fiber connector asdisclosed in Japanese Unexamined Patent Publications No. 56-110912 andNo. 56-81807, respectively.

On the other hand, matching oil, matching grease, epoxy resin or thelike is used as an optical conductor for the connection of opticalfibers in a fixed connecting device or light combining/splitting device.

It is basically required in the connection of the optical fibers tomaximally eliminate the diffusion of light at the joint portion of thetwo end faces.

However, according to the method for mechanically bringing the end facesof the optical fibers into contact with each other, an air layer isinevitably present between the end faces due to its mechanicalconstruction. Since this air layer and the cores of the optical fibershave different refractive indices, light is diffused due to a differencein refractive index, resulting in a loss of light.

An arrangement of an optical conductor between the end faces has beenproposed and put into practice in order to eliminate the air layer andprevent the loss of light.

However, the prior art method using a lens as the optical conductornecessitates a complicated construction and the use of a large-sizedapparatus and has a problem in reliability during the attachment anddetachment of the optical fibers. Thus, this method has low industrialapplicability.

The prior art method using matching oil as the optical conductor hasproblems of flow-out and oxidation of the oil resulting from increaseand decrease of temperature, and a problem of a short life.Particularly, if silicone oil is used as the matching oil, it isdifficult to prevent the silicone oil from flowing out due to itscreeping characteristic. Thus, the use of the matching oil compels anexchange of oil after a certain period of time and, therefore, has lowindustrial applicability.

On the other hand, the method using grease as the optical conductor hasbeen proposed in order to avoid the above problems of flow-out andoxidation of oil. Grease can certainly avoid an undesirable event offlow-out due to its high viscosity, but cannot avoid problems of changesin characteristics caused by temperature and a difference in refractiveindex between a thickening agent and a composition and has a lower lighttransmittance as compared to the case where the matching oil is used.Further, grease has a fatal problem of being unable to restore(eliminate) air bubbles produced by a displacement of the two end facesat the Joint portion, Therefore, grease also has low industrialapplicability.

According to the prior art method using an epoxy resin as the opticalconductor, the epoxy resin is cured by heating or air-cured, anddisplays a satisfactory performance over a long period of time. However,this method has an unavoidable problem of coloring due to oxidation. Inview of operability, mixing of B curing agent, removal of air bubbles,curing by heating, etc. are necessary during the manufacturing process.Further, in the case of defective connection of the end faces, theoptical fibers have to be thrown away and the whole process has to beresumed from the beginning. This method is used despite its poor yield,but has low industrial applicability.

In view of the problems residing in the prior art, a main object of thepresent invention is to provide a low cross-linking-density gel whichcan effectively suppress the diffusion of light when end faces of coresof optical fibers are connected, and a method for producing such a gel.

It is another object of the present invention to provide a lowcross-linking-density gel which effectively suppresses the diffusion oflight at a joint portion of end faces of cores of optical fibers, and amethod for producing such a gel.

It is still another object of the present invention to provide a lowcross-linking-density gel which is free from a flow-out problem even iftemperature increases or decreases due to a change in workingenvironments, and a method for producing such a gel.

It is further another object of the present invention to provide a lowcross-linking-density gel which can stably suppress the diffusion oflight by maintaining its working performance over a long period of time,and a method for producing such a gel.

DISCLOSURE OF THE INVENTION

In order to solve the aforementioned problems and accomplish the aboveobjects, an inventive method for producing a low cross-linking-densitygel, comprises:

a compounding step for adjusting a flexible silicone gel material tohave a specified refractive index, and

a reaction step for causing the flexible silicone gel material adjustedin the compounding step to cross-link in a binding region wherecross-linking density is low, thereby producing a lowcross-linking-density gel.

In the inventive method, the specified refractive index is setsubstantially equal to the refractive index of cores of optical fibersto be connected.

In the inventive method, a polyorganosiloxane having vinyl groups at itsends is used as a primary agent of the flexible silicone gel material.

In the inventive method, a cross-linking agent is added in the reactionstep.

In the inventive method, the polyorganosiloxane having covalently boundhydrogen atoms is added as the cross-linking agent.

In the inventive method, the compounding step end the reaction step areperformed in a clean room.

Another inventive method for producing a low cross-linking-density gel,comprises:

a compounding step for adjusting a flexible silicone gel material tohave a specified refractive index,

a combining step for synthesizing a composition by adding across-linking agent to the flexible silicone gel material adjusted inthe compounding step,

a filling step for filing the composition into a syringe,

a sealing step for sealing the syringe, and

a reaction step for heating the sealed syringe to cause the compositionto undergo an addition reaction in a binding region where cross-linkingdensity is low, thereby producing a low cross-linking-density gel in thesyringe.

In the inventive method, the syringe is sealed by mounting a cap in thesealing step.

In the inventive method, the syringe is mounted in a dispenser fordispensing a predetermined amount of the low cross-linking-density gelby replacing the cap mounted on the syringe by a nozzle after the lowcross-linking-density gel is produced in the syringe,

Further, an inventive low cross-linking-density gel is produced bycausing a flexible silicone gel material adjusted to have a specifiedrefractive index to undergo an addition reaction to cross-link in abinding region where cross-linking density is low.

In the inventive gel, the specified refractive index is setsubstantially equal to the refractive index of cores of optical fibersto be connected.

In the inventive gel, the flexible silicone gel material is apolyorganosiloxane having vinyl groups at its ends.

In the inventive gel, a cross-linking agent is added prior to thecross-linking reaction and the addition reaction takes place in thepresence of a platinum catalyst.

In the inventive gel, the cross-linking agent is a polyorganosiloxanehaving covalently bound hydrogen atoms.

In the inventive gel, the composition after being filled in the syringeis caused to undergo the addition reaction by being heated during thecross-linking reaction.

Further, the inventive low cross-linking-density gal is produced in aclean room.

SUMMARY OF THE INVENTION

A first requirement for a material used for the connection of end facesof optical fibers is that it is easily deformable like an elasticmaterial during the connection, can be formed to have an extremely smallthickness, is not allowed to flow like usual viscous matter or liquid,and does not contain in its texture anything, which hinders thepropagation of light, such as filler, dust or air bubbles havingdifferent refractive indices.

A second requirement for this material is that it is resistant tochanges in outer environments such as temperature, humidity, pressureand vibrations.

A third requirement for this material is that it does not permit dust,vapor, water and the like to intrude thereinto.

A fourth requirement for this material is that it enables an easyconnecting operation which can be completed within a short period oftime. Specifically, it is required not to increase a temperature forvacuum deaeration and curing in the connecting operation using an epoxyresin.

The inventors of the present application studied the structures ofvarious elastic materials and viscous materials during the developmentof a material which satisfies the above requirements and, in theirstudy, directed their attentions to a macromolecule having athree-dimensional reticulated structure insoluble in a solvent and a gelstructure which is a swollen material of such a macromolecule.Consequently, they established a compounding technique according towhich a transparent flexible silicone gel material selected as a basematerial among synthetic gels was gelatinized at a low cross-linkingdensity, thereby forming a low cross-linking-density gel (gel-fluidintermediate) which has a shape retaining property, which is acharacteristic of a gelatinous elastic material, while having fluidity.

As a result of repeated devotion and efforts, the inventors completed acompounding technique for producing a low cross-linking-density gelwhich satisfies all of the aforementioned requirements and found outthat this material was optimal as a material used for the connection ofend faces of optical fibers. in other words, by merely providing thethus produced low cross-linking-density gel between the end faces of theoptical fibers, a loss of light at the joint portion when light wastransmitted from one optical fiber to the other could be effectivelysuppressed and conducting efficiency was remarkably improved.

In this invention, the low cross-linking-density gel is produced asfollows.

Adjusting the refractive index by adding a primary agent and makingcross-links by adding a binding region [agent] is known to those skilledin the art. A transparent flexible silicone gel material is caused toundergo an addition reaction [in a binding agent in the binding regionwhere cross-linking density is low, with the result] resulting in a lowcross-linking density gel [with the result that the low cross-linkingdensity gel] having a viscosity and a minimum fluidity [can beobtained]. As a result of the addition reaction that provides a gelhaving a low cross-link density, in the binding region wherecross-linking density is low, free hydrogen atoms are advantageouslyabsent since they are fully consumed during the reaction.

In the above addition reaction, a polyorganosiloxane containingcovalently bound hydrogen atoms is added as a cross-linking agent to apolyorganosiloxane containing vinyl groups at its ends, which is acomponent of the primary agent, and cross-linking takes place in thepresence of a platinum catalyst.

A range of the cross-linking density was specified by an amount of thecross-lining agent to be added, and a final cross-linking density couldbe substantially precisely controlled. The cross-linked binding region[agent] of the low cross-linked density gel is in the range of 30% to10% of the theoretical quantity for the primary agent to be fullycross-linked.

If the gel is produced beyond the above cross-linked binding agent, itdisplays properties more similar to those of an elastic material as theratio of the cross-linking agent increases. As a result, the gel losesits fluidity and comes to possess a breakage point, which is notpreferable. On the other hand, if the gel is cross-linked to a lesserdegree than is recommended above, the portion of the vinyl-fractionalpolysiloxane that remains unreacted has an increased degree of freedom.

The refractive index of the low cross-linking-density gel can beadjusted to a value substantially equal to those of various opticalfibers by adjusting the refractive index of a transparent siliconeoligomer as a primary agent in advance. Thus, a loss of light caused by,the reflection and diffusion of light due to a difference in refractiveindex between the cores of the optical fibers to be connected and thelow cross-linking-density gel can be suppressed to a minimum level.

As described above, the presence of an air layer at the joint portionwhen the cores of the optical fibers are connected is not preferablebecause it brings about a loss of light. Further, a distance between theend faces of the cores is preferably as short as possible. Since theinventive gel can easily flow and be deformed upon being forciblycontacted to thereby securely eliminate an air layer between the endfaces of the cores and flatten tiny scratches and polishing streaks, itcan suppress a loss of light caused by the presence of the air layer toa minimum level.

The physical properties of such a low cross-linking-density gel and theinfluences of changes in outer environments thereon can be summarized asfollows.

(1) Temperature: wide working temperature range of −40° C. to 120° C.,(2) Humidity: moisture absorption into the component is 0%, (3) Water:water absorption into the component is 0.1% or less, (4) Dust: dustadheres to the outer surface, but does not permeate into the component,(5) Pressure: pressurized portion is free to deform, (6) Vibration:vibration does not cause dilatancy, (7) Oxidation: unoxidizable andstable against most chemicals, (8) Flow-out: does not flow out, (9)Performance: substantially semipermanently maintained.

As can be seen from the above, the low cross-linking-density gel cannotbe influenced by any outer environment except a temperature exceedingits own pyrolysis temperature and is most suitably used as an opticalconductor.

Since the low cross-linking-density gel is used in an extremely narrowarea between cores of optical fibers having a diameter of 10 to 50 μm,fine dust or like fine particles should not adhere to the surfacethereof. Further, the manufacturing process should not be performed inan environment which permits an access of foreign matters such as dust.Thus, in order to use the low cross-linking-density gel as the opticalconductor, a vessel used to produce this gel is desired to be a vessel(syringe) chosen in consideration of the manufacturing process as wellas how the gel is actually used. In other words, it is essential thatthe compounded material filled in the vessel be kept sealed until thegel is actually used after the reaction step.

Conditions required for the above vessel (syringe) are that it has atubular body which has at least inner circumferential surface thereofformed straight and is open at the opposite ends, one of the open endshas a common mount portion on which a sealing cap used during themanufacturing process and a nozzle used during the application of thegel are selectively mountable since the open end serves as a materialinjecting opening or a dispensing opening for the lowcross-linking-density gel, and a sealing packing, which serves as areceiving portion when raw materials of the low cross-linking-densitygel are filled, is movably accommodated in the vessel along itslongitudinal direction.

It should be noted that the vessel and the sealing packing can be madeof any material provided that this material does not hinder the additionreaction of the silicone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical section showing the construction of a syringefunctioning as a reaction vessel when a method for producing a lowcross-linking-density gel according to the invention is carried out,

FIG. 2 is a vertical section showing the construction of the syringefunctioning as a containing vessel for containing the produced lowcross-linking-density gel,

FIG. 3 is a vertical section showing an intermediate state when acomposition is poured into the syringe,

FIG. 4 is a vertical section showing the construction of a dispenser fordispensing a predetermined amount of the low cross-linking-density gel,and

FIG. 5 is a vertical section showing a state of the dispenser after allthe low cross-linking-density gel in the syringe was dispensed by movinga piston rod from the state of FIG. 4.

Hereinafter, a low cross-linking-density gel according to the inventionand an exemplary method for producing such a gel are described in detailwith reference to the accompanying drawings.

{Description of a Production Method}

First, an exemplary method for producing the low cross-linking-densitygel is described.

The low cross-linking-density gel used as an optical conductor forconnecting optical fibers is produced as follows. First, the refractiveindex of a transparent flexible silicone gel material, specifically atransparent silicone oligomer as a base material is so adjusted as tolie within a range of 1.43 to 1.50. A composition is produced by anaddition reaction of the thus adjusted transparent silicone oligomer anda polyorganosiloxane containing covalently bound hydrogen atoms to beadded as a cross-linking agent to the primary agent in the presence of aplatinum catalyst in a binding region where cross-linking-density is lowand an addition rate of the cross-linking agent is 30% in theoreticalequivalent.

The thus produced composition is filled into a syringe 10 shown in FIG.1, and is caused to undergo an addition reaction in a constanttemperature bath at a temperature of to 100° C. maximum for a reactiontime of from 1 hour to 6 hours. As a result, a low cross-linking-densitygel which is viscous and has a minimum fluidity despite being athree-dimensionally cross-linked material of low density is obtained inthe syringe 10.

It is preferred that such a production method is carried out in a cleanroom and that the storage of raw materials, compounding, filling intothe syringe 10 and reaction process are all carried out in the cleanroom.

{Description of the Low Cross-linking-density Gel}

The low cross-linking-density gel produced as above has the followingphysical properties:

(i) Composition: silicone mixture, (ii) Refractive Index: 1.46(adjustable within a range of 1.43 to 1.50) (iii) Working stable withina temperature range of −40° C. to Temperature Range: 120° C., (iv)Moisture/Water at most 0.1% within a temperature range of Absorption:25° C. to 100° C., (v) Dust: adhere to the outer surface, but does notpermeate into the texture, (vi) Resistance to deformable upon beingpressurized, but does not Pressure/Vibration: undergo thixotropy, (vii)Viscosity: at least 100,000 cP, (viii) Oxidizability: will not beoxidized, (ix) Chemical insoluble in most solvents, Resistance: (x)Fluidity: has no fluidity, but is freely deformable upon an externalforce, (xi) Performance at least 20 years when being kept at normalRetaining Period: temperature.

The low cross-linking-density gel having the above physical propertiesdisplays the following effects when being used as an optical conductor.

First, concerning the light transmitting property, the loss of light wasreduced and transmittance was improved by using this lowcross-linking-density gel as the optically connecting conductor at thejoint portion of the optical fibers. In this example, the loss of lightcould be reduced to about {fraction (1/10)} as compared to a case wherethe mechanical contact method is used, and transmittance was improved byabout 30%,

More specifically, results of a comparative experiment for verifying thelight transmitting property of the low cross-linking-density gel are asfollows.

Transmittance Transmittance when the low when the end cross- Polishedstate f end faces of faces were merely linking-density optical fibersbrought into contact gel was used Cut by a cutter 68.50% 90.50% Polishedby an abrasive cloth 73.28% 94.79% having a grain diameter of 0.03 mmPolished by an abrasive cloth 77.14% 97.28% having a grain diameter of0.012 mm Polished by an abrasive cloth 77.85% 99.35% having a graindiameter of 0.003 mm

Concerning the properties, the low cross-linking-density gel is anaggregate which is an intimidate of an elastic material and liquid; isviscous despite its cross-linking structure of very low density; isfreely deformable upon being pressurized; adheres to a pressurizedmaterial, and is restored to its original shape upon being released frompressure. This gel will not be softened or fluidized upon application ofheat. Since this gel has no free hydrogen atoms as a binding site, itwill not be chemically bound with the cores of the optical fibers andcomponents of a cladding and is very unlikely to hinder the propagationof light.

As a result, the low cross-linking-density gel filled as the opticalconductor at the Joint portion of the optical fibers flattens theunevenness of the end faces of the optical fibers using couplingpressure, thereby reducing the reflection and diffusion of light to aconsiderably low level, and is stable over a long period of time withoutflowing out.

In an example of experiment confirming such effects, a small amount ofthe low cross-linking-density gel was held between a pair of glassplates, which was then vertically held in a constant temperature bath at120° C. for 1000 hours. Thereafter, displacement of the glass plates wasmeasured, but the gel was confirmed to have neither been displaced norbecome fluid.

Subsequently, only about 5 mg of the low cross-linking-density gel wasfilled into an FC optical fiber connector, and optical fibers arerepeatedly attached and detached 50 times and transmittance was measuredeach time. The original transmittance was maintained up to the 20^(th)measurement, and started slightly varying thereafter. However, thisvariation was not to such an extent that practicability would behindered.

The construction of a dispenser for filling the lowcross-linking-density gel into the FC optical fiber connector and thestate of the low cross-linking-density gel filled in the dispenser aredescribed in detail later with reference to the pertinent drawings.

Further, an outer socket of the above FC optical fiber connector wasdetached, and the optical fibers were dropped into water while beingconnected by an assembly comprised only of ferrules and a sleeve.Transmittance was measured with the low cross-linking-density gelexposed to water. The obtained measurement values were stable withoutvarying independently of the elapse of time.

When boiling water was poured to a portion of the FC optical fiberconnector where the low cross-linking-density gel was exposed, a 10%reduction in transmittance was observed. However, as the temperaturereturned to room temperature, transmittance gradually returned to theoriginal value. When boiling water was poured onto the optical fibers,transmittance changed as above.

Thus, the optical conductor or the low cross-linking-density gel filledinto the joint portion of the optical fibers is sufficiently resistantto temperature, humidity, pressure, vibration, dust, water and vapor andcan contribute to simplifying the construction of the conventionallyused devices such as optical connectors, fixed connecting devices andlight combining/splitting devices, and is therefore highly industriallyapplicable.

{Description of the Syringe 10}

The aforementioned syringe 10 has following two applications.

(A) The first application is to be used as a reaction vessel in whichcomposition is filled and caused to react as shown in FIG. 1.

(B) The second application is to be used as a containing vessel in whicha nozzle 20 is mounted on the dispensing end of the syringe 10 as shownin FIG. 2 and which is assembled into the dispenser for supplying(applying) a predetermined amount of the produced lowcross-linking-density gel to the joint portion.

The construction of one embodiment of the syringe 10 used for the abovetwo applications is described in detail with reference to FIGS. 1 to 3.

First, the construction used for the first application is described withreference to FIG. 1. The syringe 10 has a tubular syringe main body 12,which is so formed as to have a straight inner surface and openings atthe opposite ends. In this embodiment, the syringe main body 12 has eventhickness and, thus, has a straight outer surface.

The left opening of the syringe main body 12 in FIG. 1 is specified tobe commonly used as an admitting opening through which theaforementioned composition 14 is admitted and a dispensing openingthrough which the low cross-linking-density gel is dispensed. Anexternal thread 14A is formed on the outer circumferential surface ofthe end where this admitting/dispensing opening is formed, and a cap 16is detachably mounted on the admitting/dispensing opening. Accordingly,an internal thread 16A is formed in the inner surface of the cap 16. Aportion between the syringe main body 12 and the cap 16 is so held as toprevent the entrance and escape of liquid with the external thread 12Aand the internal thread 16A engaged with each other.

On the other hand, a sealing packing 18 which serves as a receivingportion when the aforementioned composition 14 is fitted into thesyringe main body 12 is movably accommodated in the syringe main body 12along its longitudinal axis.

In the syringe 10 thus constructed, the cap 16 is detached as shown inFIG. 3 and the sealing packing 18 is accommodated while being shiftedtoward the left in FIG. 3 when the composition 14 is admitted. In thisstate, the composition 14 is gradually admitted into the syringe mainbody 12 through the admitting/dispensing opening. As the composition 14is admitted, the sealing packing 18 is gradually moved toward the rightby being pushed by the composition 14. After the admittance of aspecified amount of the composition 14 the cap 16 is mounted, therebycompleting the syringe 10 having the composition 14 filled therein asshown in FIG. 1.

The syringe 10 having the composition 14 filled therein is placed in anunillustrated constant temperature bath as it is and is heated underspecified heating conditions. The composition 14 in the syringe 10 iscaused to undergo an addition reaction by this heating, and becomes alow cross-linking-density gel 22.

On the other hand, when the thus produced low cross-linking-density gel22 is to be filled into the joint portion of the optical fibers, the cap16 is detached and the nozzle 20 is mounted instead in the clean room,with the result that the syringe 10 has a construction shown in FIG. 2.

Alternatively, it may be considered to suck up the lowcross-linking-density gel 22, which was obtained by an addition reactionin a separate reaction vessel, by a device like a hypodermic syringe andto inject it into the syringe 10. However, if the lowcross-linking-density gel 22 produced outside the syringe 10 is injectedinto the syringe 10, air bubbles may enter the low cross-linking-densitygel 22 during the injection, and it is extremely difficult to inject thelow cross-linking-density gel 22 into the syringe 10 while preventingthe entrance of such air bubbles.

If air bubbles should enter the low cross-linking-density gel 22 duringthe injection of the low cross-linking-density gel 22, no measures canbe taken to remove the air bubbles and the low cross-linking-density gel22 has to be thrown away as a detective gel. On the other hand, thecomposition 14 is liquid and, if air bubbles enter it, they naturallycome up if the syringe 10 is left standing. Thus, air bubbles can beremoved from the composition 14 without any problem.

From this point of view, it is fairly meaningful that the syringe 10 hasboth a function as the reaction vessel and a function as the containingvessel. In other words, particular effects can be obtained by producingthe low cross-linking-density gel 22 by the addition reaction of thecomposition 14 in the syringe 10 as a containing vessel to be assembledinto the dispenser 30 to be described later.

{Description of the Dispenser 30}

Next, the construction of the dispenser 30 for dispensing apredetermined amount of the low cross-linking-density gel 22 containedin the syringe 10 is described in detail with reference to FIGS. 4 and5.

The dispenser 30 is provided with an outer tube 32 in the form of ahollow cylinder in which the syringe 10 described above is accommodatedas shown in FIG. 4. The outer tube 32 has a closed left end and a fullyopen right end in FIGS. 4 and 5. In the middle of the left end of theouter tube 32 is formed an insertion hole 34 which extends in thethickness direction of the left end and into which the nozzle 20 mountedon the aforementioned syringe 10 is inserted. At the left side of theinner surface of the outer tube 32 is formed a step 36 with which theleft end surface of the syringe 10 accommodated into the outer tube 32comes into contact to be located in a specified position in the outertube 32.

An internal thread 32A is formed in the inner surface of the right endof the outer tube 32 in FIGS. 4 and 5. On the other hand, a mount block40 having a piston rod 38 reciprocatingly supported along itslongitudinal direction as described later is mounted in the right end ofthe outer tube 32., The outer circumferential surface of the mount block40 is divided into a left portion and a right portion, the left portionhaving a larger diameter than the right portion. On the outercircumferential surface of the left portion is formed an external thread40A spirally engageable with the internal thread 32A. The mount block 40is fixedly mounted in the outer tube 32 by the engagement of theinternal and external threads 32A and 40A.

In the center of the mount block 40 is formed a center hole 40Bextending along its longitudinal direction. A lead groove 40A isspirally formed in the inner surface of the center hole 40B. The pistonrod 38 is so inserted into the lead groove 38 as to be movable back andforth along its longitudinal direction, and has a lead groove 38Aengageable with the lead groove 40A formed on its outer surface. Sincethe piston rod 38 is supported in the mount block 40 by the spiralengagement of the lead grooves 38A, 40C, the piston rod 38 is mademovable back and forth along its longitudinal direction by being rotatedabout its longitudinal axis with the mount block 40 fixed.

The left end of the piston rod 38 is in contact with the sealing packing18 in the syringe 10 mounted in the outer side from the right side. Asthe piston rod 38 is moved to the left, it pushes the sealing packing 18to the left, thereby pushing the low cross-linking-density gel 22contained in the syringe 10 to dispense it through a dispensing openingformed at the leading end of the nozzle 20. In other words, the sealingpacking 18 functions as a cylinder head by mounting the syringe 10functioning as a containing vessel in the dispenser 30.

At the right end of the piston rod 38, a slotted-head nut 42 is fixedvia a bolt 44. On the other hand, a rotary tube 46 is so mounted as tocover the piston rod 38 from the right side. On the innercircumferential surface of the rotary tube 46 is formed a spline groove46A, which is engaged with an engaging groove 42A formed in the outercircumferential surface of the slotted-head nut 42. Thus, the piston rod38 is rotated integrally with the rotary tube 46, but is freely movablealong its longitudinal direction independently of the rotary tube 46. Inother words, by rotating the rotary tube 46 about its longitudinaldirection, the piston rod 38 is rotated together with the rotary tube 46and, as a result, is moved forward or backward along its longitudinaldirection.

A left portion of the rotary tube 46 extends up to a position where itfaces the outer surface of the small-diameter portion of the mount block40 at its right side in radial directions. In order to lock the rotarytube 46 in rotational positions spaced at specified angles, a multitudeof recesses 48 for specifying the rotational positions spaced at everyspecified angle are formed one after another in circumferentialdirection on the outer surface of the small-diameter portion of themount block 40.

The rotary tube 46 is mounted with a locking ring 50 having a leadingend selectively engageable with one of the recesses 48. The locking ring50 is made of a spring member and the leading end thereof is so set asto be elastically engageable with the recess 48. The locking ring 50specifies an angle of rotation of the rotary tube 46 and functions as aso-called snap ring for locking the rotary tube 46 so as not todisengage from the mount block 40 along the longitudinal direction.

Accordingly, the leading end of the locking ring 50 is elasticallyengaged with a certain recess 48 and, therefore, the rotary tube 46 iselastically locked in the rotational position. If the rotary tube 46 isforcibly rotated in its locked state, the leading end of the lockingring 50 is elastically deformed and comes out of the recess 48 it hasbeen engaged with. After the rotary tube 46 is rotated by a specifiedangle, this leading end is engaged with the adjacent recess 48. Sincethe rotary tube 46 is elastically held in position after being rotatedby the specified angle, the low cross-linking-density gel 22 in thesyringe 10 is dispensed through the leading end of the nozzle 20 by anamount corresponding to the rotation of the rotary tube 46.

Since the recesses 48 are circumferentially arranged at equal intervals,a fixed amount of the low cross-linking-density gel 22 is constantlydispensed by rotating the rotary tube 46 by one interval of the recesses48. This enables the dispenser 30 to dispense a predetermined amount ofthe low cross-linking-density gel 22.

If the cylinder head 18 is moved to the left end in the syringe 10 asshown in FIG. 5 by continuously rotating the rotary tube 46, it meansthat all the low cross-linking-density gel 22 in the syringe 10 has beendispensed.

In this embodiment, the rotary tube 46 is made of a transparent materialso that the position of the piston rod inside (position along thelongitudinal direction) can be visually confirmed. As a result, anoperator can roughly confirm a remaining amount of the lowcross-linking-density gel 22 in the syringe 10 upon seeing the positionof the piston rod 38.

By marking the slotted-head nut 42 secured to the piston rod 38 at itsspecified position and graduating the rotary tube 46, the remainingamount of the low cross-linking-density gel 22 is more accuratelycomprehensible.

Next, how the dispenser 30 constructed as above is assembled isdescribed.

First, the low cross-linking-density gel 22 is filled into the outertube 32 according to the aforementioned manufacturing method; thesyringe 10 having the nozzle 20 mounted at its leading end is insertedinto the outer tube 32: and the nozzle 20 is caused to project outwardthrough the insertion hole 34. Thereafter, the mount block 40 having thepiston rod 38 already mounted therein is fixed to the outer tube 32 byspirally engaging the external thread 40A and the internal thread 32A.At this stage, the piston rod 38 is located in its most retractedposition with respect to the mount block 40 lest the leading end thereofshould inadvertently come into contact with the cylinder head 18 in thesyringe 10 to thereby cause the low cross-linking-density gel 22 filledin the syringe 10 to leak from the nozzle 20.

Thereafter, the slotted-head nut 42 is secured to the rear end of thepiston rod 38 using the bolt 44, and the rotary, tube 46 is fitted fromthe right side in FIGS. 4 and 5 so that its leading end is locatedaround the outer surface of the mount block 40. Then, the locking ring50 is mounted on the outer surface of the leading end of the rotary tube46, and the leading end thereof is engaged with one of the recesses 48.In this way; the rotary tube 46 is prevented from disengaging from themount block 40 and is elastically held in the present rotationalposition.

{Description of the Optical Fiber Connector}

The construction of an FC optical fiber connector (hereinafter, merely“connector”) 60 in which the low cross-linking-density gel 22 is filledas an optical conductor using the dispenser 30 constructed as above isdescribed with reference to FIG. 6.

The construction of the connector 60 is specified by the Japanindustrial Standards (JIS). For the FC type, it is specified to fitferrules on cores 64A, 64B of two optical fibers 62A, 62B. However, inthis embodiment, the cores 64A, 64B are inserted into an opticalconductor 66 while being exposed without using the ferrules.

Specifically, this connector 60 includes a double-split adapter 68,which is a hollow cylinder having open ends. The optical conductor 66 isfitted substantially in the middle position of the center hole of theadapter 68 with respect to a longitudinal direction.

In this embodiment, the optical conductor 66 is comprised of a plasticsleeve 70 and the low cross-linking-density gel 22 filled into thesleeve 70 using the dispenser 30.

More specifically, the center hole of the adapter 68 is comprised offirst to fifth through holes 68A to 68E. The first through hole 68A islocated in the middle along the longitudinal direction and the opticalconductor 66 is closely fitted thereto. The second through hole 86B islocated adjacent to the first through hole 68 at the right side and hasa diameter smaller than that of the first through hole 86A. The thirdthrough hole 86C is located adjacent to the first through hole 86A atthe left side and has a diameter larger than that of the first throughhole 86A, and a cushion ring 72 to be described later is closely fittedthereinto. The fourth through hole 86D is located adjacent to the thirdthrough hole 86C at the left side, is open in the left end surface ofthe adapter 68 and has a diameter larger than that of the second throughhole 86C, and a first fitting 74 to be described later is detachablyfitted thereinto. The fifth through hole 68E is located adjacent to thesecond through hole 86B at the right side, is open in the right endsurface of the adapter 68 and has a diameter larger than that of thesecond through hole 68B, and a second fitting 76 to be described lateris detachably fitted thereinto.

The first and second fittings 74, 76 are so formed as to have the sameshape and to hold the outer surfaces of the optical fibers 62A, 62Bwhose cores 64A, 64B are exposed from the end surfaces of the first andsecond fittings 74, 76, respectively. The first and second fittings 74,76 are held in the adapter 68 by corresponding fixing nuts 78, 80 whilebeing fitted in the fourth and fifth through holes 68D, 68E,respectively.

How the connector 60 thus constructed is assembled is described below.

With all the parts described above being separated from each other, theoptical conductor 66 filled with the low cross-linking-density gel 22 isinserted into the center hole of the adapter 68 from the left in FIG. 6to be closely fitted into the first through hole 68A. The opticalconductor 66 is brought into contact with a step formed between thefirst and second through holes 68A and 68B to be located in a specifiedinsertion position. Similarly, the cushion ring 72 is inserted into thecenter hole from the left to be closely fitted into the third throughhole 68C. This cushion ring 72 is brought into contact with the opticalconductor 66 to hold the optical conductor 66 in its specified insertionposition.

Thereafter, the first fitting 74 bearing one optical fiber 62A is fittedinto the fourth through hole 68D from the left and is held in thisfitted state by the first fixing nut 78. With the first fitting 74fitted into the adapter 68, the leading end face of the core 64Bprojecting from the held optical fiber 62A enters the lowcross-linking-density gel 22 of the optical conductor 66 as shown inFIG. 6.

Subsequently, the second fitting 76 bearing the other optical fiber 62Bis fitted into the fifth through hole 68E from the right and is held inthis fitted state by the second fixing nut 80. With the second fitting76 fitted into the adapter 68, the leading end face of the core 54Bprojecting from the held optical fiber 62B enters the lowcross-linking-density gel 22 of the optical conductor 66 as shown inFIG. 6.

Here, in the optical conductor 66, the leading end faces of both cores64A, 64B are located in the low cross-linking-density gel 22. Projectinglengths of the cores 64A, 64B are set such that the both leading endfaces are right opposite to each other with the first and secondfittings 74, 76 properly mounted in the adapter 68. Since the projectinglength, i.e, the cut positions of the cores 64A, 64B are specified inthis way, the cut positions can be fairly roughly set as compared to acase where both end faces need to be precisely brought into contact witheach other according to the conventional mechanical contact method. As aresult, operability can be improved.

Specifically, since the low cross-linking-density gel 22 is filled inthe optical conductor 66, it is present between the both end faces ofthe cores 64A, 64B even if these end faces are not closely facedopposite to each other. Thus, as described above, a loss of the lighttransmitted from one optical fiber 62A to the other 62B at the jointportion in this connector 60 can be maximally suppressed by the lowcross-linking-density gel 22 present between the end faces.

It should be noted that the present invention is not limited to theconstruction and assembling procedure of the aforementioned embodiment,and a variety of modifications can be made without departing from thespirit and scope of the present invention.

For example, although the optical conductor 66 is comprised of thesleeve 70 and the low cross-linking-density gal 22 filled in the sleeve70 in the foregoing embodiment, the present invention is not limitedsuch a construction. The optical conductor may be formed only of the lowcross-linking-density gel 22 without using the sleeve 70.

Further, although the low cross-linking-density gel 22 is filled intothe sleeve 70 of the optical conductor 66 to be mounted in the connector60 using the dispenser 30 in the foregoing embodiment, it may be filledusing a gel injecting apparatus having an other construction accordingto the present invention,

What is claimed is:
 1. A method for producing a flexible and low densitycross-linking gel for connecting optical fibers having a refractiveindex, said method comprising: adjusting the refractive index of aflexible silicone gel material to be that generally equal to therefractive index of said optical fibers to be connected, and a reactionstep for causing the flexible silicone gel material adjusted in saidadjusting step by cross-linking said silicone gel material to an extentsuch that a gel having a low degree of cross-linking is produced forclosely adhering to optical fibers; and wherein said adjusting step andsaid reaction step are carried out in a clean room.
 2. A method forproducing a low cross-linking density gel used for connecting and foradhering to optical fibers, said method comprising adjusting therefractive index of a flexible silicone gel material to that of saidoptical fibers to be connected, synthesizing a composition by adding across-linking agent to said adjustable flexible silicone gel material;filing a syringe with said composition; sealing said syringe; andheating said sealed syringe to cause said composition to undergo anaddition reaction thereby producing a low cross-linking density gel insaid syringe allowing close adherence to said optical fibers.
 3. Amethod according to claim 2, wherein the syringe is sealed by mounting acap in the sealing step.
 4. A method according to claim 3, wherein thesyringe is mounted in a dispenser for dispensing a predetermined amountof the low cross-linking-density gel by replacing the cap mounted on thesyringe by a nozzle after the low cross-linking-density gel is producedin the syringe.